The morphogenesis of peripheral sense organs, known as rays, in the tail of the C. elegans male will be studied by means of a combined genetic, cellular, and molecular approach. Nine bilateral pairs of rays are present at reproducible sites, forming a species-specific pattern in the tail. The strategy to be taken to understand the generation of this pattern comprises three steps: 1) Defining the determinative cellular events that govern generation of the pattern, 2) Isolating and studying mutants, identifying both the morphogenetic and regulatory genes and gene products that participate in determinative cellular events, and 3) Learning how morphogenetic and regulatory genes interact in a morphogenetic pathway. The long term goal of this research is to understand how genes specify the form of multicellular animals. Three aspects of ray development are addressed: 1. Number of rays. The number of rays is determined by the specification of a subset of cells that express the ray sublineage. The sublineage generates two neurons and a support cell, which differentiate into a ray during the last larval stage. In order to understand how initiation of the ray sublineage is controlled, a genetic and molecular analysis of the lin- 32 gene, a key gene for entry into the neurogenic branch of the ray sublineage, will be carried out. In order to learn how regulation of expression of the ray sublineage differs in different cell lineages, a similar analysis of the mab-19 gene, a gene required for expression of the ray sublineage by a subset of related cells, will be carried out. Preliminary analysis of eight mutations that block development of rays will be completed, with particular emphasis on determining the cell lineage defects, if any, in these mutants. 2. Generation of ray differences. Although they rise from a stereotyped cell sublineage, the nine bilateral pairs of rays differ from each other with respect to morphology, ultrastructure, neurotransmitter usage, interactions with neighboring cells during development, and genetic requirements. Laser ablation experiments will be carried out to define cellular interactions that determine differences between the rays. Genetic and molecular studies will be undertaken on five genes postulated to be required for establishing the wild type pattern of ray differences. 3. Formation of a specific spatial arrangement of rays. A genetic and molecular characterization will be carried out on the gene hypothesized to participate during morphogenesis in interactions of ray cells required for their correct positioning within the epidermis.